Preparatory Surveys

We will conduct two surveys in preparation for parallax observations.

1) A VLA snapshot mapping of ~400 water masers to obtain recent spectra and absolute positions. We started with the Arcetri Catalog (Valdettaro et al 2001, A&A, 368, 845) and selected only those listed as from star forming regions (SFR). A small number of sources far from the Galactic plane, presumably low-mass SFRs or stellar masers, were removed. The source list and results for the survey can be obtained by clicking here.

Based on the survey results, we will select targets for parallax observation.

2) We will search for background calibrators (presumably QSOs with compact radio emission). Calibrator candidates within about 1.5 degrees from a target maser and stronger than about 10 mJy will be obtained from unresolved sources in the CORNISH or NVSS surveys. We will observe these candidates with the VLBA at X-band and make visibility versus baseline-length plots (as in the VLBA calibrator lists). The results of the calibrator survey can be obtain by clicking here.

Resolved sources are likely to be Galactic HII regions, whereas compact sources will have brightness temperatures above 10^7 K and, hence, non-thermal sources. Almost all non-thermal sources will be extragalactic AGN and suitable for parallax reference sources.